During the past year, the research efforts of this section focused on Entamoeba histolytica and related Entamoebae in the following areas: 1) Development of a new medium for the axenic culture, 2) nutritional immunity, especially the role played by iron in the production of lesions in experimental animals and the manifestation of disease in human subjects, 3) evaluation of the virulence potential of individuals comprising populations of amebae (strains) through studies of the amebal clones in the Mattern-Keister neonatal hamster model, 4) investigation of the possible role of the viruses of E. histolytica in virulence conversion of the amebae, 5) investigation of a variety of parameters to improve cryopreservation of E. histolytica at the temperature of liquid nitrogen vapor. BIBLIOGRAPHIC REFERENCES: Weinbach, E.C., Harlow, D.R., Claggett, C.E. and Diamond, L.S.: Entamoeba histolytica: Diaphorase activities. Exp. Parasitol. 41: 186-197, 1977. Mattern, C.F.T., and Keister, D.B.: Experimental Amebiasis I. Pathogenicity of Axenically Cultured Entamoeba histolytica in the Brain of the Newborn Mouse. Am. J. Trop. Med. Hyg. 26: 393-401, 1977.